A geographic information system (GIS) database contains data associated with selected objects positioned within a geographic area. Data contained in the GIS database typically includes absolute or relative positional data associated with the selected objects as well as data representative of various attributes of the objects themselves. Data forming a GIS database can be quickly accessed and manipulated as desired. Data which forms a GIS database must first be collected, stored and then converted by GIS software into a GIS database. Both the geographic positions of the selected objects and the attributes of the objects must be collected and stored. Several different techniques may be used to collect the data.
With respect to the collection of the data, conventional surveying techniques may be utilized obtain the positional data associated with the objects. Some conventional surveying techniques utilize a manual theodolite; other conventional surveying techniques utilize a total station. By its very nature, conventional surveying techniques generally require two persons to work together to obtain the requisite positional data. Technical surveying expertise is required to obtain the requisite positional data. Also, when a manual theodolite is utilized, once the positional data associated with an object is obtained, the positional data is recorded manually. Data representative of attributes associated with the objects is also manually recorded. The positional data and the data representative of the attributes are thereafter entered into and stored in a computer database.
While positional data obtained through conventional surveying techniques is relatively accurate, conventional surveying techniques require technical expertise, are labor intensive, and are comparatively slow and expensive. Moreover, structured attribute entry of the data representative of the attributes together with the positional data is usually not possible, particularly when a manual theodolite is utilized. Several steps are required to store the data and the data is not stored in a manner to facilitate usage thereof by GIS software utilized to form a GIS database.
Positional data associated with the objects may also be obtained through the use of aerial photography. Aerial photographs taken of a geographical area may, however, include only those objects which are actually visible from the air. The aerial photograph may thereafter be digitized through the use of a computer scanner and entered into a computer database. Positional data associated with the objects visible in the aerial photograph relative to the overall geographical area may thereafter be accurately ascertained. Data representative of attributes associated with the visible objects may then be separately entered into the computer database. GIS software then accesses the data to form the GIS database.
As previously described, while positional data associated with the objects visible in the aerial photograph are accurate relative to the geographical area encompassed by the aerial photograph, to be included in the GIS database, the object must necessarily be visible from the air. If viewing of the object in the aerial photograph is obstructed, such as by a tree or by a building, the object cannot be identified and data representative of attributes associated with it cannot be stored. Therefore, if data associated with the object is to be stored in the GIS database, the data must be obtained in another manner. Also, even if the object is visible from the air, attributes associated with the object frequently are not. Viewing of the object from a ground location is therefore oftentimes still necessary in order to determine the attributes associated with the object.
SAFCO (tm) Corporation of 6060 Northwest Highway, Chicago, Ill. 60631 markets a WALKABOUT PCS (tm) system having a GRIDPAD (tm) hand-held computer and a laser-ranging distance/bearing measurement instrument for in-building navigation. The measurement instrument generates positional information which is stored in the computer. The system monitors the signal strengths of radio frequency signals, such as those generated in a cellular communication system. When positioned at a desired location, the signal strengths of radio frequency signals are measured and provided to the hand-held computer. The system does not provide for determination of positional data associated with remotely positioned objects and for entry of data associated with the remotely-positioned objects.
U.S. Pat. No. 5,214,757 ("'757") describes a system in which positional data associated with an object is obtained through the use of a Global Positioning System ("GPS") receiver operative in conjunction with the GPS satellites of the Global Positioning System. As therein described, the GPS receiver is coupled directly to a GPS computer, and the GPS receiver together with the GPS computer is positioned immediately proximate to a selected object as to which data is to be stored. Once positional data associated with the object is ascertained by the GPS receiver, the data is supplied directly to the GPS computer. The GPS computer, in turn, is coupled to a GIS computer which receives the data processed by the GPS computer. GIS software embodied in the GIS computer is operative to convert the stored data into a GIS database. When the GPS receiver is mounted on a motorized vehicle, the path of a roadway, for instance, may be plotted as the motorized vehicle travels along the roadway.
The GPS receiver is operative to provide accurate positional data relating to the location of the GPS receiver when positioned to receive signals generated by the GPS satellites of the global positioning system. However, if the GPS receiver is positioned at a location where signals from the GPS satellites are occluded, such as in a wooded or mountainous area, the GPS receiver cannot receive the positional signals generated by the GPS satellites. Under these conditions, the GPS receiver is simply not operational for generating accurate positional data for subsequent processing by the GPS computer. Moreover, in addition to those situations in which the operation of the GPS receiver is precluded by the immediate proximity of trees or mountains, positioning the GPS receiver adjacent to buildings in certain urban environments presents the same problems when buildings are of such a height to occlude portions of the sky. And, because the GPS receiver must be positioned immediately proximate to each selected object, a large amount of time is required to obtain the necessary positional data when positional data is to be obtained for large numbers of objects.
As previously noted, the system described in the '757 patent requires the GPS receiver to be positioned immediately proximate to each object as to which data is to be stored. In addition to the possible occlusion of the requisite GPS satellites, when data must be obtained for a large number of objects, the need to position the GPS receiver immediately proximate to each of the objects requires a significant amount of time and effort. As a result, the system described in the '757 patent may be inconvenient to utilize in determining the positional information of a relatively large number of features and, depending on the surrounding terrain, it may actually not permit the necessary positional data to form a GIS database to be obtained.
In light of the foregoing, it can be seen that existing techniques by which data may be collected all suffer from various disadvantages. It is with respect to these considerations and other background information relative to the determination and storage of data utilized by GIS software to form a GIS database that the significant improvements of the present invention have evolved.